In recent years, a lithium ion battery has been widely developed as a power supply of an electric vehicle, an electric motorcycle, a forklift, an automatic guided vehicle, an uninterrupted power supply (UPS) unit, a power storage facility, an emergency electric power supply unit, and the like. In response to such a trend, it is desirable to develop a lithium ion battery having a large scale, a large capacity, a high output power, and a low resistance. Meanwhile, in order to guarantee a cycle life over 10 years, for example, it is desirable to provide a structure sufficiently endurable to vibration or impact even in a large scale. As a casing of the battery, typically, a metal can or a casing made of an aluminum-containing laminate film may be employed. The laminate film casing is applied to a large-scaled battery or a thin battery because it guarantees freedom in shaping and does not necessitate an expensive mold unlike a metal can.
The lithium ion battery comprising the laminate film casing has also been developed as a power supply for use in the fields described above. However, the lithium ion battery comprising the laminate film casing is susceptible to vibration or impact because it does not have sufficient rigidity compared to the metal can.